The art of marking road surfaces is well trafficked and widely known. The marks, most commonly traffic lines, can be painted on the road surface, or formed thereon by applying liquid or molten material thereto, or provided thereon by applying and adhesively securing manufactured marking tapes. The formed or applied traffic lines or any other marks will thereafter form a part of the road surface and will be correspondingly subjected to the wear and destructive action of traffic. A continuing goal in the pavement-marking industry is to find economical products from which to form traffic control stripes having a longer useful life than the commonly used painted stripes.
One type of product comprises paints based on epoxy resins. These provide a longer life than some other paints, but nevertheless have achieved only a small usage, probably because some epoxy paints cure slowly, and elaborate and expensive application procedures may be required. Also, the applied lines frequently tend to spall and crack, show little impact resistance, and discolor with age.
Thicker coatings, such as thermoplastic polymers extruded or sprayed while in a liquid or molten condition, have produced some increase in life because of the greater amount of material to be worn away. However, the increased amount of material also increases the cost of the markings, and both expensive equipment and inconvenient procedures are required to apply them. Also, the high profile of these markings can be disturbing to passing traffic, and the lines are especially susceptible to removal by snowplow blades. Such markings will also tend to spall, especially when applied to concrete, apparently because of the mismatch of thermal expansion characteristics between the rigid thick markings and the concrete.
Roadmarks consisting of preformed tapes or strips are well known in the art to be advantageous in comparison to the conventional traffic aids described above. Preformed marking tapes are typically formed from a composite structure comprising a support base of calendared rubber compound, a self adhesive bottom layer, and a top-coat anti-wear layer incorporating anti-skid material and light retro-reflective elements. Such a composite structure is disclosed in many patents, such as U.S. Pat. Nos. 3,782,843, 3,935,365, 3,399,607, 4,020,211, 4,117,192, and 4,990,024.
However, this kind of marking tape still shows less than desired durability. Marking tapes comprising a support of unvulcanized elastomer and a top-coat of polyurethane having a high capacity to be deformed, high permanent set, and low elastic return are disclosed in the art as suitable materials to obtain a superior durability. These marking tapes deform readily into intimate contact with irregular pavement surfaces, absorb the energy of wheel impacts without fracture and avoid the stretch-return action that has been found to loosen marking tapes from a roadway pavement. Typical examples of such marking tapes can be found in U.S. Pat. Nos. 4,117,192 and 4,990,024. A negative aspect of such a deformable marking tape relates to its low mechanical properties, in particular a low tensile strength, a low 10% modulus and too high a level of elongation. The term "10% modulus", as used herein, means the load (expressed in kg/cm.sup.2) to be applied to the marking tape to have a 10% elongation relative to its initial length.
U.S. Pat. No. Re. 31,669 discloses the use of a non-woven material interposed between a support and a polyurethane top-coat to obtain a stiffer, less deformable, and less temperature sensitive marking tape. However, such a construction tends to have a high elastic return which, under the action of traffic, promotes the detachment of the tape from the roadway.
Italian Patent Application No. MI 003213/91A discloses the use of a support base comprising a saturated acrylonitrile butadiene elastomer grafted with a zinc salt of (meth)acrylic acid to improve the mechanical characteristics.
Accordingly, in spite of much work in the field of preformed marking tape, there is still the need of an improved marking tape that shows a high permanent set with moderate elongation, high mechanical properties, and low temperature sensitivity. There is still the need for an improved marking tape that shows long durability under any weather and traffic conditions.